The present invention relates to a method for determining the temperature of a semiconductor chip, and to a semiconductor chip with a temperature measuring configuration.
As storage densities are progressively increasing, chip areas are continuously being reduced and operating frequencies are continuously being raised. As a result, the energy density introduced into the semiconductor material is increasing. A considerable power loss is generated during the operation of the chip, for example of a DRAM and a SDRAM. This causes the chips to heat up to a temperature that may be considerably higher than the ambient temperature. However, the behavior of the chip module is adversely affected by excessively high temperatures. Therefore, quantitative knowledge of the semiconductor chip temperature is of interest for various reasons. There is therefore a need to determine it. However, this is known to be difficult using conventional methods for temperature measurement, i.e. temperature measurements using temperature sensors, in particular if the measurement is to be carried out on a semiconductor chip which is being operated according to regulations, i.e. is accommodated in a housing and is being operated in a specific circuit.
Published, Non-Prosecuted German patent application DE 196 52 046 A1 discloses a method for determining the temperature of a semiconductor chip in which the following method steps are described. Selected chip terminals have voltages applied to them, or currents impressed on them. The polarity and/or dimensioning of the voltages or currents is such that the current flow which occurs and/or the voltage which occurs is at least partially determined by a diode provided between the selected chip terminals or a structure which acts as a diode. The voltage and current values that occur are determined and the temperature of the semiconductor chip is determined by reference to the determined voltage and current values using a current/voltage temperature relationship that has been previously determined for the semiconductor chip or semiconductor chip type which is to be investigated. Here, use is made of the known effect that the current flowing across a pn-type junction or through a diode (with a permanently set voltage) or the voltage which occurs at the diode (with an impressed current) depends on the temperature of the diode or its pn-type junction. This dependence makes it possible to determine, from the voltage applied to the selected diode and the current flowing through it, the temperature of the diode in a precise way. The diodes that are used for the measurement do not need to be specifically provided for this purpose, but may also be present in any case on the semiconductor chip. Such diodes are, for example, overvoltage protection diodes or polarity-reversal protection diodes. Structures which act as diodes may alternatively or additionally be used as the temperature measuring diodes. Such structures are generated automatically if the semiconductor chip substrate is provided with wells with different doping.
In order to standardize the temperature measuring configuration integrated onto the chip, the chip or chip type which is to be investigated must have been previously characterized in terms of the currents flowing, or voltages occurring, at the various chip temperatures. To do this, for example, measurements of currents or voltages that occur are carried out on the semiconductor chip that has been successively heated through an external source to predefined temperatures. The chip that is to be characterized is first placed in a temperature-controlled measuring space and placed at a defined temperature in the non-operative state. At a time at which it can be assumed that the semiconductor chip has reached a defined temperature, the semiconductor chip is activated in such a way that either the diode or the diode is switched on. The voltage applied to the input signal terminal and the current which consequently flows via the input signal terminal or the current which is impressed on the input signal terminal and the voltage which occurs as a result of this are determined and assigned to the defined temperature. If this measuring and assignment process is repeated for various temperatures, a current/voltage temperature characteristic curve is obtained, from which the chip temperature can be precisely determined later by reference to measured current and/or voltage values. It is generally favorable here if the power loss generated by the temperature measurement in the semiconductor chip is kept as low as possible. If the semiconductor chip continues to be operated normally during the temperature measurement, it also proves advantageous if the semiconductor chip is operated during the temperature measurement in such a way that the occurrence of power losses which may change the temperature which is actually to be measured is restricted as far as possible.
If the semiconductor chip temperature is to be measured at a given time during the xe2x80x9cnormalxe2x80x9d operation, it is necessary, during normal operation, to apply a voltage to, or impress a current on, the input signal terminal. The polarity and dimensioning of the voltage or current are such that one of the diodes is thus placed in the conductive state and the current or voltage that occurs is determined by the diode which has been switched on. The voltage and current values that occur in this process are, as described above, used for determining the temperature. The semiconductor chip terminal which is selected as the input signal terminal is preferably one which can have a measuring voltage applied to it, or a measuring current impressed on it, without having to disrupt or interrupt the xe2x80x9cnormalxe2x80x9d operation of the semiconductor chip.
Furthermore, the manual titled xe2x80x9cElektrische Messtechnik [Electrical Measuring Technology]xe2x80x9d, by E. Schrxc3xcfer, Carl Hanser Verlag [Publishing House], Munich Vienna, 1983, discloses a method for measuring small ohmic resistances. Here, a known current is impressed on a resistor and a voltage dropping across the resistor is measured. The contact resistances that occur at the terminals when measuring very small resistances should not be neglected. In order to avoid including them in the measurement, four-conductor connection technology is used. Here, the terminals and of the power supply circuit are separated from the potential terminals of the measuring line. The possible voltage drops at the connecting points are not measured. The contact resistances at the terminals are in series with the input resistance of voltage meter and can be ignored, as can the resistances of the measuring lines, as long as the voltage meter has sufficiently high impedance.
It is accordingly an object of the invention to provide a method for determining the temperature of a semiconductor chip and a semiconductor chip with temperature measuring configuration which overcome the above-mentioned disadvantages of the prior art devices and methods of this general type, in which the temperature can be determined easily and with a high precision.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for determining a temperature of a semiconductor chip. The method includes the steps of impressing a defined current onto selected chip terminals, and measuring a voltage occurring at least partially at a semiconductor diode structure disposed between the selected chip terminals using four-conductor connection technology, the voltage being tapped off directly at the semiconductor diode structure. The temperature of the semiconductor chip is determined by reference to the voltage and the defined current.
The temperature measuring circuit with which the actual chip temperature can be determined precisely during the normal or active operation of the chip by four-conductor measuring technology is processed on the chip. The voltage fluctuations brought about during the active operation, for example owing to ground bounces, cause measuring errors that are negligible according to the invention. The measuring circuit according to the invention can be connected into the circuit here either by a test mode and switching transistors or of transfer gates or by a metal option.
Semiconductor switches, which can for example be activated by a control circuit integrated on the chip, are advantageously provided in the connecting lines and/or in the measuring lines of the temperature measuring circuit. In order to feed in the measuring current and to measure the voltage value by an external test configuration for determining the chip temperature during active operation, the temperature measuring configuration of the chip is first activated. To do this, the switches integrated on the chip are closed. As a result, the temperature measuring configuration is accessible externally via the chip measuring terminals. After the temperature measurement has been terminated, these switches can be opened again in order to be able to make available the measuring terminals again for normal use of the chip. The temperature measurement can therefore be carried out at any desired chip on a wafer, or even in a housed chip.
According to one preferred embodiment, the address or input/output terminals of the module which are present in any case, and which are connected to corresponding address or input/output lines, are used as the four diode chip terminals. If the control circuit and the switches are integrated onto the chip, these terminals can be used as address and input/output terminals during normal operation without restricting the use, while in test mode they are temporarily used as measuring terminals for temperature measurement. Chip internal connection pads or fixed voltage potentials may also be used as chip terminals.
With the foregoing and other objects in view there is provided, in accordance with the invention, a semiconductor chip containing a housing, chip terminals extending from the housing, a diode structure having terminals disposed in the housing, two connecting lines each connected between one of the chip terminals and one of the terminals of the diode structure, and two voltage measuring lines each connected between further ones of the chips terminals and the terminals of the diode structure. The connecting lines and the voltage measuring lines connected to the diode structure using four-conductor connection technology.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for determining the temperature of a semiconductor chip and a semiconductor chip with temperature measuring configuration, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.